Bulletin of the Geological Society of Malaysia, Volume 49, April 2004, pp. 157-167
1School of Environmental Science and Natural Resources, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, MALAYSIA
2Geological Engineering Department, Faculty of Engineering, Gadjah Mada University, Yogyakarta, INDONESIA
Abstract: Breccia dominated rocks outcropping in the Tanjung Murau – Tanjung Sekakap area have been deposited in a composite system of alluvial fans and Gilbert-type deltas. The sedimentary facies ranges from boulder-dominated facies at the bottom to gravelstone-sandstone-dominated facies at the top of the succession. Other recognized facies are disorganized boulder-cobble-supported breccia (Bd), crudely stratified cobble-boulder-rich breccia (Bs), crudely stratified cobble-rich gravelstone (Gs-1), disorganized clast-supported gravelstone (Gd), crudely stratified pebble-rich gravelstone (Gs-2), normally-inversely-graded gravelstone (Gn-i), crossbedded gravelstone (Gc), stratified sandstone (Ss), massive sandstone (Sm) and homogenous mudstone (Mh) facies. Alluvial fan association feature discontinuous breccias and gravelstones (facies Bd and Bs), where sheet-floods and debris flows are dominant. The gravelstone dominated facies Gd, Gs-1 and Gs-2 intercalated with facies Gc are associated with the topset–foreset of a Gilbert-type fan-delta. The Gilbert-type topset are represented by facies Gc, Gn-i and Gs-2 as well as facies Ss. The dominance of breccia and gravelstone facies of alluvial fan and Gilbert-type topset – foreset delta facies associations suggest that these sediments were deposited on a steeply sloping continental margin with a rate of deposition similar to the rate of subsidence.